Automotive automatic transmission

ABSTRACT

An automotive automatic transmission comprises a transmission mechanism which includes a casing, an output shaft and a clutch drum. The clutch drum is spline-connected to the output shaft to rotate therewith. A final drive mechanism is arranged to which a torque of the output shaft is transmitted. A parking gear is integrally formed on a cylindrical outer surface of the clutch drum, and a parking pawl is pivotally held by the casing. The parking pawl is engageable with the parking gear to lock the same.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to automatic transmissions formotor vehicles, and more particularly to automotive automatictransmissions of a type which is equipped with a park-lock mechanism.

2. Description of the Prior Art

One of conventional automotive automatic transmissions of theabove-mentioned type is shown in Japanese Patent First ProvisionalPublication 60-84469. In this transmission, a parking gear whichconstitutes part of the park-lock mechanism is integral with an inputgear mounted on one end of a countershaft of the transmission. Essentialparts of the transmission are arranged about a main shaft which iscoaxial with the crankshaft of the engine, and the countershaft isarranged in parallel with the main shaft. The torque from the engine istransmitted through the input gear to the countershaft and the torque ofthe countershaft is transmitted through a final drive gear mounted onthe other end of the countershaft to a final drive mechanism. That is,the parking gear is integrally and coaxially formed on one side surfaceof the input gear of the countershaft. When a parking pawl pivotallyheld by a transmission casing is engaged with the parking gear, thecountershaft is locked and thus drive wheels of the motor vehicle arelocked.

However, provision of the parking gear on the side surface of the inputgear of the countershaft tends to increase the entire length of thecountershaft and thus cause a longitudinally bulky construction of thetransmission. In fact, such elongated countershaft narrows an effectivespace for accommodating other parts of the transmission.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anautomotive automatic transmission which is free of the above-mentioneddrawback.

According to the present invention, there is provided an automotiveautomatic transmission in which the parking gear is integrally formed ona cylindrical outer surface of a clutch drum of the transmission.

According to a first aspect of the present invention, there is providedan automotive automatic transmission which comprises a transmissionmechanism including a casing, an output shaft and a clutch drum, theclutch drum being connected to the output shaft to rotate therewithrelative to the casing; a final drive mechanism to which a torque of theoutput shaft is transmitted; a parking gear which is formed on acylindrical outer surface of the clutch drum; and a parking pawl whichis pivotally held by the casing and engageable with the parking gear tolock the same.

According to a second aspect of the present invention, there is providedan automotive automatic transmission which comprises a torque converter;a main transmission mechanism including an input shaft to which a torqueis transmitted from the torque converter, an intermediate output shaftand first and second planetary gear units coaxially disposed about theintermediate output shaft to transmit the torque of the input shaft tothe intermediate output shaft while changing the rotation speed ratiotherebetween; a sub-transmission mechanism including a casing, an inputgear powered by the intermediate output shaft, an output shaft, a thirdplanetary gear unit coaxially disposed about the output shaft totransmit the torque of the input gear to the output shaft while changingthe rotation speed ratio therebetween and a clutch drum incorporatedwith the third planetary gear unit, the clutch drum being connected tothe output shaft to rotate therewith; a final drive mechanism to which atorque of said output shaft is transmitted; a parking gear which isformed on a cylindrical outer surface of the clutch drum; and a parkingpawl which is pivotally held by the casing and engageable with theparking gear to lock the same.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will becomeapparent from the following description when taken in conjunction withthe accompanying drawings, in which:

FIG. 1 is a schematic illustration of an automotive automatictransmission according to the present invention;

FIG. 2 is a TABLE showing ON/OFF condition of various friction elementsof the transmission when the transmission assumes certain speeds; and

FIG. 3 is a sectional view of a sub-transmission mechanism of thetransmission.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, there is schematically shown an automotive automatictransmission according to the present invention.

The transmission comprises generally a torque converter 10, a maintransmission mechanism 1, a sub-transmission mechanism 2 and a finaldrive mechanism 3.

The torque converter 10 converts a torque of an engine output shaft 12and transmits the converted torque to an input shaft 13.

The main transmission mechanism 1 comprises the input shaft 13 to whichthe converted engine torque is fed, an intermediate output shaft 14 fromwhich a drive power is transmitted to the sub-transmission mechanism 2,a first planetary gear unit 15, a second planatary gear unit 16, a frontclutch 20, a rear clutch 22, a low-and-reverse brake 26, a band brake 28and a low one-way clutch 30. The first planetary gear unit 15 comprisesa sun gear S1, an internal gear R1, pinion gears P1 meshed with both thesun and internal gears S1 and R1 and a pinion carrier PC1 carrying thepinion gears P1, and the second planetary gear unit 16 comprises a sungear S2, an internal gear R2, pinion gears P2 meshed with both the sunand internal gears S2 and R2 and a pinion carrier PC2 carrying thepinion gears P2. The parts are arranged in the illustrated manner. Theband brake 28 is equipped with both a servo-apply chamber SA foreffecting engagement of the band brake 28 and a servo-release chamber SRfor effecting disengagement of the band brake 28. The servo-releasechamber SR has a pressure receiving area larger than that of theservo-apply chamber SA.

The sub-transmission mechanism 2 comprises a third planetary gear unit31, a direct clutch 32 and a reduction brake 33. The third planetarygear unit 31 comprises a sun gear S3, an internal gear R3, pinion gearsP3 meshed with both the sun and internal gears S3 and R3 and a pinioncarrier PC3 carrying the pinion gears P3. The internal gear R3 isengaged with the intermediate output shaft 14 through mutually meshedgears 37 and 38, and thus the torque of the intermediate output shaft 14is transmitted to the internal gear R3. The sun gear S3 is connectableto the pinion carrier PC3 through the direct clutch 32. Furthermore, thesun gear S3 is connectable to a fixed portion (viz., casing 66) throughthe reduction brake 33. A one-way clutch 36 is arranged in parallel withthe reduction brake 33. The pinion carrier PC3 is constantly engagedwith an output shaft 35. The output shaft 35 is equipped with a drivepinion 39 to which a final drive gear 40 of the final drive mechanism 3is engaged.

By operating the clutches 20 and 22 and the brakes 26, 28 and 33 invarious combinations, operation conditions of the first, second andthird planetary gear units 15, 16 and 31 are changed and thus therotation speed ratio of the output shaft 35 relative to the input shaft13 is changed. That is, by engaging or disengaging the clutches 20, 22and 32, the brakes 26, 28 and 33 and the one-way clutches 30 and 36 in amanner as shown in the TABLE of FIG. 2, four forward speeds and onereverse are obtained by the transmission. In the TABLE, the mark "o"indicates an "engaged condition" of the corresponding friction element,and the mark "(o)" indicates an "engaged condition" which takes placeonly when a shift lever of the transmission is in "L(low)range".

In FIG. 3, there is shown a sectional view of the sub-transmissionmechanism 2 of the transmission.

As shown, the gear 38 of the mechanism 2 is constantly meshed with theoutput gear 37 of the main transmission mechanism 1. The gear 38 isconnected with the internal gear R3 to form a single unit. The gear 38is rotatably supported by a casing 54 through a bearing 53. The pinioncarrier PC3 is spline-connected to a clutch drum 55 to rotate integrallytherewith. The clutch drum 55 is spline-connected to the output shaft 35of the sub-transmission mechanism 2 to rotate integrally therewith.

It is to be noted that the clutch drum 55 is formed on a cylindricalouter surface thereof with a parking gear 90. As is shown in FIG. 3, theouter diameter of the parking gear 90 is smaller than that of thelargest diameter part (viz., the part indicated by the arrow 32) of theclutch drum 55. As shown in FIG. 3, a parking pawl 100 is pivotally heldby a casing 66 of the sub-transmission mechanism 2 near the parking gear90. That is, the parking pawl is engageable with the parking gear 90 tolock the same.

The output shaft 35 is integrally formed with the drive pinion 39 whichis meshed with the final drive gear 40. The output shaft 35 is rotatablysupported by a casing 61 through bearings 59 and 60.

The clutch drum 55 has a piston 62 slidably received in a cylinderportion thereof. Upon energization, the piston 62 can apply a suitableengaging force to clutch plates 63 of the clutch 32. When the clutchplates 63 are thus engaged, a hub 64 rotated integrally with the sungear S3 becomes to rotate together with the clutch drum 55. That is,when the piston 62 is pressed by a hydraulic power in a direction toengage the clutch plates 63, the pinion carrier PC3 and the sun gear S3are coupled to rotate together like a single unit.

As shown in FIG. 3, the sun gear S3 has at its Left end a hub plate 65secured thereto. The hub plate 65 is connectable to the casing 66through the reduction brake 33. The reduction brake 33 comprises apiston 67 and brake plates 68. The brake plates 68 comprise a firstgroup of plates spline-connected to the hub plate 65 and a second groupof plates spline-connected to the casing 66, these plates being arrangedalternately. Thus, when the piston 67 is pressed by a hydraulic power ina direction to engage the brake plates 68, the hub plate 65 becomesfixed to the casing 66.

The casing 66 has at its center part a boss portion 70 on which an innerrace 71 of the one-way clutch 36 is mounted. That is, the inner race 71is spline-connected to a cylindrical outer surface of the boss portion70, and axial displacement of the inner race 71 is suppressed by aninner wall of the casing 66 and a snap ring 72. Around the inner race71, there is mounted a wedge structure 73. Around the wedge structure73, there is mounted an outer race 74. Between a space defined betweenleft surfaces of the outer race 74 and the wedge structure 73 and aninner surface of the casing 66, there is disposed a bearing 75. A rightend portion of the wedge structure 73 is in contact with the hub plate65. A right end surface of the outer race 74 is formed with a pluralityof projections 74a which are engaged with corresponding openings formedin the hub plate 65. The remaining portion of the right end surface ofthe outer race 74, which is free of the projections 74a, is in contactwith the hub plate 65. Because of engagement of the projections 74a ofthe outer race 74 with the openings of the hub plate 65, the outer race74 and the hub plate 65 can rotate together like a single unit.

In the following, operation of the sub-transmission mechanism 2 will bedescribed with reference to FIG. 3.

When, with the direct clutch 32 kept disengaged, a torque is transmittedfrom the gear 37 to the gear 38, the internal gear R3 is forced torotate in a given direction. However, due to the work of the one-wayclutch 36 incorporated with the hub plate 65, the sun gear S3 issuppressed from making a rotation in the direction identical to that ofthe internal gear R3. Thus, under this condition, the pinion carrier PC3is rotated at a reduced speed and the rotation of the pinion carrier PC3is transmitted through the clutch drum 55 to the output shaft 35. Withthis, a speed reduction is effected by the sub-transmission mechanism 2.When an engine brake is carried out, the one-way clutch 36 runs idle.Thus, at such engine brake, the reduction brake 33 is engaged to fix thehub plate 65, and thus, the speed reduction is also achieved.

When the direct clutch 32 is engaged and the reduction brake 33 isdisengaged, the sun gear S3 and the pinion carrier PC3 are coupled torotate together like a single unit, and the internal gear R3 is rotatedtogether with them. Accordingly, the rotation of the gear 38 is directlytransmitted to the output shaft 35 without making a speed differencetherebetween. Thus, a so-called "direct connection" is effected in thesub-transmission mechanism 2.

When a shift lever (not shown) of the transmission is moved to a parkingposition, the parking pawl 100 is brought into engagement with theparking gear 90 to lock the same. Since the clutch drum 55 on which theparking gear 90 is formed is spline-connected to the output shaft 35,the locking of the parking gear 90 locks the output shaft 35 and thuslocks the drive wheels (not shown) of the associated motor vehicle.

What is claimed is:
 1. An automative automatic transmission comprising:atransmission mechanism including a casing, an output shaft and a clutchdrum, said clutch drum being connected to said output shaft to rotatetherewith relative to said casing: a final drive mechanism to which atorque of said output shaft is transmitted; a parking gear formed on acylindrical outer surface of said clutch drum, said parking gear beingintegral with said clutch drum; and a parking pawl which is pivotallyheld by said casing and engageable with said parking gear to lock thesame, wherein the outer diameter of said parking gear is smaller thanthat of the largest diameter part of said clutch drum.
 2. An automotivetransmission as claimed in claim 1, in which said clutch drum isarranged to achieve a direct connection between an input element of saidtransmission mechanism and said output shaft.
 3. An automotive automatictransmission as claimed in claim 1 in which said clutch drum is of anintegral body which has a fluid-filled piston chamber defined therein.4. An automotive automatic transmission as claimed in claim 3, in whichsaid clutch drum and said output shaft are connected by means of aspline connection.
 5. An automotive automatic transmission comprising:atorque converter; a main transmission mechanism including an input shaftto which a torque is transmitted from said torque converter, anintermediate output shaft and first and second planetary gear unitscoaxially disposed about said intermediate output shaft to transmit thetorque of said input shaft to said intermediate output shaft whilechanging the rotation speed ratio therebetween; a sub-transmissionmechanism including a casing, an input gear powered by said intermediateoutput shaft, an output shaft, a third planetary gear unit coaxiallydisposed about said output shaft to transmit the torque of said inputgear to said output shaft while changing the rotation speed ratiotherebetween and a clutch drum incorporated with said third planetarygear unit, said clutch drum being connected to said output shaft torotate therewith; a final drive mechanism to which a torque of saidoutput shaft is transmitted; a parking gear formed on a cylindricalouter surface of said clutch drum, said parking gear being integral withsaid clutch drum; a parking pawl which is pivotally held by said casingand engageable with said parking gear to lock the same, wherein theouter diameter of said parking gear is smaller than that of the largestdiameter part of said clutch drum.
 6. An automotive automatictransmission as claimed in claim 5, in which said clutch drum of thesub-transmission mechanism is of an integral body which has afluid-filled piston chamber defined therein.
 7. An automotive automatictransmission comprising:a transmission mechanism including a casing, anoutput shaft and a clutch drum, said clutch drum being connected to saidoutput shaft to rotate therewith relative to said casing; a final drivemechanism to which a torque of said output shaft is transmitted; aparking gear formed on a cylindrical outer surface of said clutch drum;and a parking pawl pivotally held by said casing and engageable withsaid parking gear to lock the same, wherein said clutch drum and saidoutput shaft are connected by means of a spline connection.